Cosmetic or dermatological preparations in the form of emulsions, PIT emulsions and preparations comprising washing-active substances are widespread. Emulsions may be W/O or O/W emulsions or else multiple emulsions, i.e. emulsions containing more than two phases. They are sold in the form of creams, lotions, but also as perspiration-inhibiting, body-odour-reducing cleansing and sunscreen preparations. PIT emulsions are particular forms of emulsions. They are characterized by the method of their preparation and the droplet sizes resulting therefrom. For the preparation, emulsifiers or emulsifier systems are used which change their polarity depending on the temperature, meaning that phase inversion arises during the preparation. As a result of this phase inversion, particular product properties are achieved, such as, for example, a particular optical appearance or an extraordinarily low viscosity. Such preparations are suitable, for example, as sprayable skincare or sunscreen emulsions. Finally, preparations comprising washing-active substances are used as body- or hair-cleansing compositions, and also as dishwashing detergents.
Usually, such preparations are prepared in a batchwise process, mostly in a mixer into which the starting substances are introduced and the intermediate or end product are removed after a certain operating time. In this process, all of the process steps which are required for the preparation of the product take place in this one apparatus one after the other: metering, mixing, heating/cooling, emulsifying, cooling. Often, upon removing the product, the product is subjected to subsequent homogenization. Although in food technology continuous plants for the preparation of emulsions such as yoghurt or mayonnaise are widespread, cosmetic or dermatological preparations are only prepared continuously in exceptional cases. This is because the requirements on the stability of cosmetic products are much higher and, due to their more complex composition comprising numerous different components, said products are much more difficult to prepare in stable form. Thus, for example, for a yoghurt, a stability in the region of a few weeks is expected, whereas cosmetic emulsions should be stable over at least 30 months.
Plants which are operated in batchwise processes have a series of disadvantages besides the advantageous flexibility with regard to the products which can be prepared. The long batch times required lead to increased production costs. There is a risk of contamination since the plants have to be emptied and charged frequently. The risk of contamination can be limited by keeping the product temperatures low. This is achieved by using cold aqueous phases. Alternatively, a heat exchanger can also be connected downstream. In most cases, relatively large amounts of air are introduced into the system, which is undesirable.
Known continuous processes are characterized in that the individual phases are metered into a high-performance emulsifying device at the same time. The emulsification and homogenization operation takes place therein with a high input of energy, giving rise to high shear forces. However, the occurrence of high shear forces is able to damage polymers present in the preparations. As a result of simultaneously metering all of the components, they are subjected to relatively high temperatures over prolonged periods. As a result, the use of temperature-sensitive substances is only possible to a limited degree. Such substances are, for example, cosmetic active and functional ingredients, such as fragrances, vitamins, coenzymes, peptides, enzymes, nucleic acids, plant extracts, preservatives, such as, for example, those from 1,2-dibromo-2,4-dicyanobutane and 2-phenoxyethanol.
Although continuous plants with which it is possible to prepare a large number of different cosmetic and/or dermatological preparations are desired, they are not known to date. In particular, a plant with which it would be possible to prepare both low-viscosity emulsions, lotions, creams and body- and hair-cleansing preparations and also dishwashing detergents would represent a significant improvement in the prior art.
It has hitherto not been possible to prepare PIT emulsions in continuous processes since the droplets remain too large despite a high input of energy. Continuously prepared creams and liquid emulsions were in most cases insufficiently stable. During the preparation of preparations comprising washing-active substances, the use of continuous processes in most cases leads to inhomogeneities arising as a result of inadequate mixing. Transparent preparations are therefore only obtainable with difficulty since such inhomogeneities often lead to clouding. For the preparation of O/W emulsions, continuous processes have hitherto not been able to penetrate the market since it has not been possible to achieve products of high quality: in most cases the emulsions were not stable or tended towards oil losses. The cause of this behaviour is assumed to be the fact that homogeneous droplet size distributions cannot be achieved through the use of static mixers on their own.
The article “Eine Anlage zum kontinuierlichen Emulgieren” [A continuous emulsification plant] in the Journal Verfahrenstechnik, volume 1-2 from 1986 describes, for example, a continuous preparation process for the preparation of W/O and O/W creams. The discontinuously prepared preproducts pass through a metering system, a dynamic mixer and a static mixer. Here, a hot/cold process is realized in which the preproducts enter the process in cold or hot form. The emulsion is produced in the dynamic mixer, homogenization takes place in the static mixer, as a result of which the particle size distribution is adjusted. This plant is suitable for the preparation of skin creams, body lotions, mayonnaise and sauces.
In this process, the homogenization operation takes place at 40 to 75° C., although it would be desirable to carry out this step at low temperatures since temperature-sensitive constituents of the formulations, such as odour or aroma substances or active ingredients such as vitamins, should as far as possible not be subjected to thermal stress.